1. Field of the Invention
The present invention relates to a method of forming a wear-resistant dielectric layer, and more particularly, to a method of forming a wear-resistant dielectric layer by performing a plasma enhanced chemical vapor deposition (PECVD) process in a high frequency/low frequency alternating manner.
2. Description of the Prior Art
In the fabrication of semiconductor devices and MEMS (micro electromechanical system) devices, a dielectric layer mainly provides insulation and protection functions. For different purposes, some parameters of the dielectric layer, such as the electric constant, the material strength, and the stress between the dielectric and other materials that contact with the dielectric layer, must be considered. Generally, the dielectric layer is made of silicon oxide and silicon nitride. Silicon oxide has a higher electric constant, and the stress between silicon oxide and other semiconductor materials, e.g. a silicon substrate, is less. Consequently, silicon oxide is frequently used as a material of a gate insulating material. On the other hand, silicon nitride is more rigid, and therefore is mostly selected as a passivation layer of the semiconductor devices or the MEMS devices. For a passivation layer, wear-resistant and hydrophilic characteristics are required.
The stress between silicon nitride and other semiconductor materials is higher, and thus the thickness of a silicon nitride layer formed by deposition technique has its limit. Otherwise, cracking or peeling problems tend to appear. Normally, the stress of a silicon nitride layer exceeds 1000 MPa as long as the thickness of the silicon nitride layer is over several micrometers. In view of the high stress problem, the thickness of a silicon nitride layer is generally less than 1 micrometer.